The present invention relates to a brake force regulator for a motorcycle interconnected hydraulic brake system including a control piston, which is slidable in response to the pressure from a hand cylinder, adapted to reduce the brake pressure of a pedal-actuated rear-wheel brake by arranging for the control piston to be movable into a fluid inlet chamber connected with the pedal cylinder, such movement being caused by the pressure from the hand cylinder under increase in volume of a fluid outlet chamber connected with the rear-wheel brake, the control piston having a fluid passageway including a closure member through which the fluid inlet chamber is connectible with the fluid outlet chamber. A brake force regulator of this type is described in German Patent DE-OS 2,558,825.
In motorcycles, a rear-wheel lock leads to the vehicle tending to turn about its vertical axis, as is the case in the event of a locked condition of the rear wheels of a four-wheeled vehicle. Therefore, overbraking of the rear wheel must be avoided. In the brake system disclosed in German Patent DE-OS 2,558,825, this is achieved by the provision of a stepped piston of simple design which is displaced responsive to the pressure in the front-wheel brake, thereby reducing the pressure in the rear-wheel brake. In this manner, the brake force at the rear wheel is reduced in response to the shift of weight to the front wheel caused by the additional actuation of the front-wheel brake.
Though this prior known brake force regulator is of simple construction, it has the disadvantage that the stepped piston is displaced on actuation of the front-wheel brake even when the rear-wheel brake is not applied. This causes the stepped piston to draw fluid from the rear-wheel brake. The result is inevitably an increased brake clearance when the rear-wheel brake is actuated. The case may even be that, upon repeated actuation of the front-wheel brake, the stepped piston of the brake force regulator operates in the manner of a pump evacuating the rear-wheel brake of fluid to such an extent that pressure is unable to be developed in the rear-wheel brake no matter how far the pedal is depressed.
To eliminate this disadvantage, a motorcycle brake system has been proposed in copending U.S. Patent application Ser. No. 916,630, filed June 19, 1978 of H. H. Luepertz, having the same assignee as the present application, a brake force regulator including a slidably sealed first piston forming on one end a boundary for an inlet chamber connected with the pedal cylinder and on the other end a boundary for an outlet chamber connected with the rear-wheel brake, a passageway in the first piston adapted to be closed by a valve closure member which is preloaded in the open position and urged by the pedal-cylinder pressure in the closing direction, and a rod bearing upon the first piston in the outlet chamber, the rod being linked to a second piston subjected to the hand-cylinder pressure in the direction towards the first piston. From the point of view of its function, this brake force regulator admittedly represents an advance over the brake force regulator disclosed in German Patent DE-OS 2,558,825, its construction is, however, substantially more complicated. If the fluid connection from the pedal cylinder to the rear-wheel brake is to be interrupted by the hand-cylinder pressure, it is necessary to displace elements having a total of three seals. This necessitates a high response force.